Methods and Arrangements in a Telecommunication System for Configuring Transmission of Sounding Reference Signals

ABSTRACT

A base station in a communications network broadcasts a cell-specific instruction to a plurality of mobile terminals in a cell served by the base station. The cell-specific instruction indicates that an uplink symbol has been semi-statically configured for aperiodic sounding reference signal (SRS) transmission over multiple subsequent subframes. The base station dynamically determines that a first mobile terminal of the plurality of mobile terminals is to use the uplink symbol for SRS transmission in a given one of the multiple subsequent subframes. In response, the base station signals a first terminal-specific instruction to the first mobile terminal. The first terminal-specific instruction is distinct from the cell-specific instruction and indicates that the first mobile terminal is to use the uplink symbol for SRS transmission in the given subframe.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/370,649 filed Feb. 10, 2012, which is acontinuation application of U.S. patent application Ser. No. 13/256,595filed Sep. 14, 2011, and issued as U.S. Pat. No. 8,817,719, which is aU.S. National Stage application of International Patent App. No.PCT/SE2010/050,685 filed Jun. 18, 2010, which in turn claims priorityfrom U.S. Provisional App. No. 61/306,606 filed Feb. 22, 2010, thedisclosures of all of which are incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to methods and arrangements fortransmission of sounding reference symbols (SRS).

BACKGROUND

Sounding reference signals (SRS) are one type of reference signals thatare transmitted by mobile terminals so that the base station canestimate the uplink channels used by the mobile terminal. In the contextof Long Term Evolution (LTE) the mobile terminals are referred to asUser Equipments (UEs) and the base stations are referred to eNBs. Thechannel estimates may be used for uplink scheduling and link adaptationbut also for downlink multiple antenna transmission, especially in caseof TDD (Time Division Duplex) in LTE where the uplink and downlink usethe same frequencies. The sounding reference signals are in part definedin technical specification 3GPP TS 36.211 and have time duration of asingle OFDM (Orthogonal Frequency Division Multiplex) symbol. In theuplink of LTE system a special type of OFDM, called DFTS-OFDM (DiscreteFourier Transform Spread OFDM), is used.

Sounding reference signals can be transmitted in the last symbol of a 1ms uplink subframe. This is illustrated in FIG. 1 where a frame of 10 msis shown. Each frame is divided into 10 subframes and one subframe cancarry 12 or 14 symbols depending on whether a normal cyclic prefix orextended cyclic prefix is used. In LTE, the uplink symbols are DFTS-OFDM(Discrete Fourier Transform Spread-Orthogonal Frequency DivisionModulation) symbols which also are referred to as SC-FDMA (SingleCarrier-Frequency Division Multiple Access).

For the case with TDD, the sounding reference signals can also betransmitted in the special time slot called UpPTS, which is the uplinkpart of a special subframe. The special subframe further comprises adownlink part, DwPTS, and a guard period. The length of UpPTS can beconfigured to be one or two symbols. FIG. 2 shows an example for TDDwith 3 downlink subframes, 2 uplink subframes within a 10 ms radioframe. Up to eight symbols may be set aside for the sounding referencesignals.

The configuration of SRS symbols, such as SRS bandwidth, SRS frequencydomain position, SRS hopping pattern and SRS subframe configuration areset semi-statically as a part of RRC information element defined in thetechnical specification 3GPP TS 36.331. There are in fact two differentconfigurations: (1) Cell specific SRS configuration, which is furtherdescribed in 3GPP TS 36.211; and (2) UE specific configuration, which isfurther described in 3GPP TS 36.213.

The cell specific configuration indicates to all UEs in a cell in whichsubframe the last symbol of the subframe, or the special slot referredto as UpPTS, can be used for sounding.

In normal uplink subframes, PUSCH (Physical Uplink Shared Channel)transmission which overlaps in the frequency domain with a cell specificsubframe will be shortened in the sense that the last uplink symbol isnot used for data transmission in the uplink. Furthermore, in subframeswhere cell specific SRS resources have been reserved, terminals in thecell should use shortened PUCCH (physical Uplink Control Channel) formatwhen transmitting ACK/NACK or scheduling requests, which is referred toas formats 1a/1b/1. The shortened PUCCH format implies that the lastsymbol in the subframe is not used for transmission of controlinformation. There are also certain rules that should be applied whenthe UE shall transmit the SRSs. For example, the UE shall not transmitan SRS in a subframe where a CQI (channel quality indication) reportusing PUCCH format 2 is transmitted.

The UE specific configuration is as the name indicates UE specific andindicates to the terminal a pattern of subframes and frequency domainresources to be used for the SRS. The UE specific configuration alsoindicates other parameters that the UE shall use when transmitting theSRS, such as frequency domain comb and cyclic shift.

This means that SRSs from different terminals can be multiplexed in thetime domain, by transmitting the SRS in different subframes.Furthermore, within the same symbol, sounding reference signals can bemultiplexed in the frequency domain. The set of subcarriers is dividedinto two sets of subcarriers, or combs with the even and odd subcarriersrespectively in each such set. Additionally, the UEs may have differentbandwidth to get additional Frequency Division Multiplexing (FDM). Thecomb enables frequency domain multiplexing of signals with differentbandwidths and also overlapping. Additionally code division multiplexing(CDM) can be used. Then different users can use exactly the same timeand frequency domain resources by using different shifts of a basic basesequence. An example illustrating the multiplexing possibilities isgiven in FIG. 3 where it is shown how SRS from different users can bemultiplexed in the frequency domain and the time domain.

In LTE Rel-8/Rel-9, resources for transmission of sounding referencesignals are reserved on a cell level by higher layers. Users in a cellare then semi-statically configured to transmit sounding referencesignals using the resources reserved in the cell. When resources arereserved for sounding, they are taken from the cell and hence from alluser in the cell. As a result regardless of whether there is a need forthe UEs to sound the channel or not, the resources are taken from allusers and can not be used for data transmission.

In a cell with a certain number of users, the period of SRS transmissionis specified by the number of users and the bandwidth of SRS. When alarge number of users share the SRS resources, the SRS period mightbecome too large for some users, such as users with fast changingchannels who need more frequent update from their channels, while forsome other users this period may be too frequent.

SUMMARY

It can be noted that semi-static configuration of SRS transmission isinflexible, in a sense that resources can not be prioritized accordingto the current needs of a UE. It is therefore an aim of the embodimentsof the present invention to provide a more flexible configuration of SRStransmission.

This is achieved by dynamically triggering a mobile terminal to transmitSRS. Thus, embodiments of the invention allow dynamically trigged SRS inany uplink subframe, even without necessarily reserving resourcessemi-statically on cell level. This is done by signaling to the terminalwhether the mobile terminal should leave a predefined uplink symbolempty for sounding reference signals or use it for data transmission. Incase a terminal leaves the predefined uplink symbol empty for soundingreference signals, there are two possibilities, either the UE shalltransmit one or several reference signals from one or several antennas,or the terminal shall leave the predefined uplink symbol blank sinceanother terminal may be using the resource for sounding.

Accordingly, in a specific embodiment, there are at least threedifferent messages that can be conveyed to the terminal: use thepredefined uplink symbol for data, leave it blank or use it for soundingreference signals.

According to a first aspect of embodiments of the present invention, amethod in a base station for dynamically triggering a mobile terminal totransmit SRS is provided. A predefined uplink symbol of an uplinksubframe is configured to be used by the mobile terminal for SRS. In themethod, it is determined whether the mobile terminal shall use thepredefined uplink symbol for data transmission or not during uplinktransmission. It is then signaled to the mobile terminal instructionwhether the mobile terminal shall use the predefined uplink symbol fordata transmission or not during uplink transmission. The signaledinstruction further comprises information whether the mobile terminalshall use the predefined uplink symbol for SRS or leave the predefineduplink symbol blank if the predefined uplink symbol shall not to be usedfor data transmission.

According to a second aspect of embodiments of the present invention, amethod in a mobile terminal for dynamically transmitting SRS isprovided. A predefined uplink symbol of an uplink subframe is configuredto be used by the mobile terminal for SRS. In the method, the mobileterminal receives instruction whether the mobile terminal shall use thepredefined uplink symbol for data transmission or not during uplinktransmission. The received instruction further comprises informationwhether the mobile terminal shall use the predefined uplink symbol forSRS or leave the predefined uplink symbol blank if the predefined uplinksymbol shall not to be used for data transmission. In subsequent stepsthe mobile terminal determines whether to send data or not in thepredefined uplink symbol based on the received instruction, andtransmits in the uplink according to said determination.

According to a third aspect of embodiments of the present invention abase station for dynamically triggering a mobile terminal to transmitSRS is provided. A predefined uplink symbol of an uplink subframe isconfigured to be used by the mobile terminal for SRS. The base stationcomprises a processor configured to determine whether the mobileterminal shall use the predefined uplink symbol for data transmission ornot during uplink transmission, and a transmitter configured to signalto the mobile terminal instruction whether the mobile terminal shall usethe predefined uplink symbol for data transmission or not during uplinktransmission. The signaled instruction further comprises informationwhether the mobile terminal shall use the predefined uplink symbol forSRS or leave the predefined uplink symbol blank if the predefined uplinksymbol shall not to be used for data transmission.

According to a fourth aspect of embodiments of the present invention, amobile terminal for dynamically transmitting SRS is provided. Apredefined uplink symbol of an uplink subframe is configured to be usedby the mobile terminal for SRS. The mobile terminal comprises a receiverconfigured to receive instruction whether the mobile terminal shall usethe predefined uplink symbol for data transmission or not during uplinktransmission. The received instruction further comprises informationwhether the mobile terminal shall use the predefined uplink symbol forSRS or leave the predefined uplink symbol blank if the predefined uplinksymbol shall not to be used for data transmission. The mobile terminalfurther comprises a processor configured to determine whether to senddata or not in the predefined uplink symbol based on the receivedinstruction, and a transmitter configured to transmit in the uplinkaccording to said determination.

An advantage with embodiments of the present invention is that it ispossible to achieve flexibility in using SRS whenever it is needed. Thusany uplink subframe can be used for SRS, not only subframes in which SRSresources are reserved semi-statically.

A further advantage with embodiments of the present invention is thatuser-based SRS assignment is provided, which is more fair towards userswith no need for SRS transmission.

A yet further advantage with embodiments of the present invention isthat it is avoided to reserve resources for SRS when no need for SRSexists. That implies that more resources for SRS can be given to thosemobile terminals that need to send SRS more frequently.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a frame in which a sounding reference signal istransmitted.

FIG. 2 illustrates an example of a frame for time division duplexing(TDD).

FIG. 3 illustrates an example of multiplexing sounding reference signalsfrom different users in the frequency domain and the time domain.

FIG. 4 illustrates an example of using a fourth symbol in a subframe forsounding reference signal transmission.

FIG. 5 is a block diagram of a base station configured to dynamicallytrigger a mobile terminal to transmit sounding reference signalsaccording to one or more embodiments.

FIG. 6 illustrates an example of using a predefined uplink symbol fordata transmission according to one or more embodiments.

FIG. 7 illustrates an example of a mobile terminal transmittingadditional sounding reference signals according to one or moreembodiments.

FIG. 8 illustrates an example of a mobile terminal leaving a predefineduplink symbol blank according to one or more embodiments.

FIG. 9 illustrates an example of mobile terminal uplink schedulingaccording to one or more embodiments.

FIG. 10 is a logic flow diagram of a method in a base station accordingto one or more embodiments.

FIG. 11 is a logic flow diagram of a method in a mobile terminalaccording to one or more embodiments.

FIG. 12 is a block diagram of a base station and a mobile terminalconfigured according to one or more embodiments.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the invention. However, it will be apparent tothose skilled in the art that the invention may be practiced in otherembodiments that depart from these specific details. In other instances,detailed descriptions of well-known devices, circuits, and methods areomitted so as not to obscure the description of the invention withunnecessary details.

The present invention is exemplified in the following non-limitingdescription of embodiments of the invention. Moreover, the followingembodiments are described in the context of an LTE network but theembodiments of the present invention can also be applied in othernetworks.

It should also be noted that although a predefined uplink symbol to beused for SRS transmission is exemplified as the last symbol, thepredefined uplink symbol could be any predefined uplink symbol in asubframe. In FIG. 4, the fourth symbol is exemplified as the predefineduplink symbol. In addition since the embodiments of the invention areexemplified in the context of LTE, the uplink symbols are DFTS-OFDMuplink symbols. It should however be understood by a person skilled inthe art that the embodiments of the present invention are not limited toDFTS-OFDMA.

As stated above, in existing LTE networks e.g. LTE release 8/9, SRS istransmitted over a semi-statically assigned bandwidth and periods. Infuture networks the number of UE antennas per user will increase, whichimplies that the resources for SRS become scarcer. This requires a moreefficient management of the available resources for SRS and moreimportantly to avoid reserving resources which are only seldom used.

In addition, depending on the time-variation and frequency selectivityof the channels as well as due to the burstiness of the traffic, someUEs or some antennas of a UE may need to get a more frequent update oftheir channels than other. However, there is typically only a need forSRS when there is traffic to be transmitted in accordance to the trafficburstiness.

To address the need for more flexible SRS configuration, methods andarrangements for dynamically configuring SRS transmission based on thecurrent situation are provided. By using embodiments of the presentinvention dynamic UE specific SRS configuration can be done on anysubframe.

FIG. 5 illustrates an embodiment of the present invention. The basestation 501 of FIG. 5 is configured to dynamically trigger the mobileterminal 502 to transmit sounding reference signals (SRS) wherein apredefined uplink symbol, such as an DFTS-OFDM symbol, of an uplinksubframe is configured to be used by the mobile terminal for SRS. Thatis achieved by the base station 501 by determining whether the mobileterminal shall use the predefined uplink symbol for data transmission ornot during uplink transmission. In situations when the channel changesrapidly e.g. due to time-variation and frequency selectivity of thechannel and when the traffic is bursty, SRS transmission is requiredmore frequently than in other situations. Thus, this is taken intoaccount when the base station determines whether the mobile terminalshall use the predefined uplink symbol for data transmission or notduring uplink transmission. Then the base station 501 signals 503 to themobile terminal instruction whether the mobile terminal shall use thepredefined uplink symbol for data transmission or not during uplinktransmission. The signaled instruction further comprises informationwhether the mobile terminal shall use the predefined uplink symbol forSRS or leave the predefined uplink symbol blank if the predefined uplinksymbol shall not to be used for data transmission. As illustrated inFIG. 5, the signaled instruction of “0” 503 a implies send data, “11”503 b implies send SRS and “10” 503 c implies that the predefined uplinksymbol should be left blank. Based on the received instruction 503, themobile terminal configures its uplink transmission accordingly 504.

Hence, three cases of dynamic SRS configurations need to be signaled tothe UEs. In the first alternative, the base station signals to themobile terminal to not puncture the data on the predefined uplinksymbol, i.e. to send data. In the second alternative, the base stationsignals information to the mobile terminal to puncture the data on thepredefined uplink symbol, i.e. to send no data, and this informationcomprises further to send SRS according to the second alternative and toleave the predefined uplink symbol blank according to the thirdalternative. To signal these three alternatives, only two bits areenough as shown in FIG. 5.

It should be noted that there is no need to have a hierarchicalstructure when composing the instruction as illustrated in FIG. 5, butthat there are at least three different messages that can be sent fromthe base station to the mobile terminal. Furthermore, it is alsopossible to envision that the mobile terminal is configured with a setof different SRS parameters so that different messages can be used totransmit SRS parameters, for example of different bandwidths or withdifferent positions in the frequency domain. To exemplify, theinstruction signaled to the mobile terminal may comprise the followingalternatives: (1) Transmit data on PUSCH also in the predefined uplinksymbol; (2) Do not transmit any data on PUSCH in the predefined uplinksymbol, leave it empty; (3) Do not transmit any data on PUSCH in thepredefined uplink symbol. Instead, transmit an SRS in the predefineduplink symbol with bandwidth b1, comb c1, cyclic shift s1 and frequencydomain starting position f1; and (4) Do not transmit any data on PUSCHin the predefined uplink symbol. Instead, transmit an SRS in the lastsymbol with bandwidth b2, comb c2, cyclic shift s2 and frequency domainstarting position f2.

Turning now to FIG. 10 and FIG. 11, where flowcharts of the methods inthe base station and the mobile terminal, respectively, are illustrated.As shown in FIG. 10 a method in a base station for dynamicallytriggering a mobile terminal to transmit SRS is provided. A predefineduplink symbol of an uplink subframe is configured to be used by themobile terminal for SRS. In a first step the base station determines 301whether the mobile terminal shall use the predefined uplink symbol fordata transmission or not during uplink transmission. In a next step, thebase station signals 302 to the mobile terminal instruction whether themobile terminal shall use the predefined uplink symbol for datatransmission or not during uplink transmission. The signaled instructionfurther comprises information whether the mobile terminal shall use thepredefined uplink symbol for SRS or leave the predefined uplink symbolblank if the predefined uplink symbol shall not to be used for datatransmission.

A method in a mobile terminal for dynamically transmitting SRS is shownin FIG. 11. As stated above, a predefined uplink symbol of an uplinksubframe is configured to be used by the mobile terminal for SRS. Themobile terminal receives 310 instruction whether the mobile terminalshall use the predefined uplink symbol for data transmission or notduring uplink transmission. The received instruction further comprisesinformation whether the mobile terminal shall use the predefined uplinksymbol for SRS or leave the predefined uplink symbol blank if thepredefined uplink symbol shall not to be used for data transmission. Themobile terminal interprets the received instruction to determine 311whether to send data or not in the predefined uplink symbol based on thereceived instruction, and transmits 312 the SRS in the predefined uplinksymbol according to said determination.

The instruction signaled from the base station and received at themobile terminal may either be valid for the predefined uplink symbol ofone subsequent uplink subframe or for the predefined uplink symbol ofmultiple subsequent uplink subframes.

The predefined uplink symbol may by default be used for datatransmission, or by default be used for SRS. If the predefined uplinksymbol is by default used for SRS, by the current mobile terminal, or byother mobile terminals wherein the predefined uplink symbol is leftblank by the current mobile terminal, the signaling 302 to the mobileterminal is performed if the predefined uplink symbol should be used fordata transmission. Whether the current mobile terminal should send SRSor leave it blank such that the predefined uplink symbol can be used byother mobile terminals, can be instructed by the base station.

However, if the predefined uplink symbol is by default used for datatransmission, the signaling 302 to the mobile terminal is performed ifthe predefined uplink symbol should not be used for data transmission,which implies that the signaled instruction from the base station to themobile station comprises information whether the mobile terminal shouldsend SRS or leave it blank for other mobile terminals.

Accordingly, with reference to FIG. 12, the base station 401 comprises aprocessor 410 configured to determine whether the mobile terminal 402shall use the predefined uplink symbol for data transmission or notduring uplink transmission, and a transmitter 412 configured to signalto the mobile terminal 402 instruction 415 whether the mobile terminal402 shall use the predefined uplink symbol for data transmission or notduring uplink transmission. The signaled instruction 415 furthercomprises information whether the mobile terminal shall use thepredefined uplink symbol for SRS or leave the predefined uplink symbolblank if the predefined uplink symbol shall not to be used for datatransmission. In addition, the base station comprises a receiver 411 forreceiving the uplink transmission from the mobile terminal 402.

According to an embodiment of the present invention, the transmitter 412is configured to signal to the mobile terminal the instruction 415 asdownlink control information carried by the physical downlink controlchannel.

Moreover, the mobile terminal comprises a receiver 420 configured toreceive instruction 415 whether the mobile terminal 402 shall use thepredefined uplink symbol for data transmission or not during uplinktransmission. The received instruction further comprises informationwhether the mobile terminal 402 shall use the predefined uplink symbolfor SRS or leave the predefined uplink symbol blank if the predefineduplink symbol shall not be used for data transmission. The mobileterminal 402 further comprises a processor 440 configured to determinewhether to send data or not in the predefined uplink symbol based on thereceived instruction, and a transmitter 430 configured to transmit theSRS in the predefined uplink symbol according to said determination.

In accordance with one embodiment of the present invention, the receiver420 is configured to receive the instruction 415 as downlink controlinformation carried by the physical downlink control channel.

In case of dynamic configuration, the information whether the mobileterminal shall use the predefined uplink symbol for data transmission ornot during uplink transmission e.g. sent in an uplink scheduling grantwhich is part of downlink control information (DCI) format 0. The DCI iscarried by physical downlink control channel (PDCCH), which is sent overthe 1-4 OFDM symbols in each subframe. This means that the dynamic ofSRS configuration can have a resolution as high as every subframe.

The dynamically configured reference signals according to embodiments ofthe present invention can for example be mapped to every secondsubcarrier in the frequency domain, as in the case for the soundingreference signals defined for Release 8/9 in LTE using a so calledrepetition factor of 2, or be mapped to every subcarrier, which is thecase with the uplink demodulation reference signals for Release 8/9 inLTE. SRSs associated with different mobile terminal antennas may be codedivision multiplexed using different cyclic shifts of a certainsequence, such as a Zadoff Chu sequence.

For LTE, a 10 ms radio frame is divided into ten subframes with durationof 1 ms, and in each 1 ms subframe, 12 or 14 DFTS-OFDM symbols aretransmitted depending on whether normal or extended cyclic prefix lengthis used as illustrated in FIGS. 1 and 4. As stated above, thedynamically configured SRSs does not have to be transmitted in the lastuplink symbol of subframe, but the symbol can be predefined as well asdynamically or semi-statically configured in any of the uplink symbols.It should also be noted that not only one uplink symbol but severaluplink symbols can be used.

The dynamically configured SRS according to embodiments of the presentinvention can be self-contained, which implies that the SRS istransmitted within the resources assigned for data transmission, i.e.PUSCH resources. Also, RRM (Radio Resource Management) parameters may beconfigured such that the configuration parameters for the dynamic SRS ofthe invention can be the same as the ones for periodic SRS transmissionand the configuration can be done semi-statically as a part of RRC(Radio Resource Control) information elements.

Thanks to the dynamically configured aperiodic SRS provided byembodiments of the present invention, SRS transmissions can be requestedwhen there is a need for sounding. The base station is then able todynamically request transmission of an SRS in a certain subframe. Forexample that can be done as part of an uplink grant so that the SRS istransmitted in the same subframe as the data. The signaled instructionmay comprise parameters which can be semi-statically configured and mayalso be a function of the subframe, be partially determined by the PUSCHallocation, or be partially dynamically signaled in the uplink grant.

However, if the cell specific resource has not been reserved, otherusers may transmit data in the predefined uplink symbol of the subframe,and this would then collide with the SRS transmission. Hence accordingto embodiments of the invention, the mobile terminal can also bedynamically instructed to leave the last symbol empty to allow foranother mobile terminal to transmit an SRS without any overlap.

In another case, the cell may have reserved resources, e.g. the lastsymbol, for SRS, and this means that existing mobile terminals, e.g. LTErelease 8/9 UEs, must leave the last symbol empty and hence less symbolscan be used for data transmission. At the same time, a mobile terminalaccording to the present invention could, if instructed by the basestation, use these resources for data transmission. The allocation ofthe SRS resources is under the control of the base station which knowsif SRS will be transmitted from any users in the cell. Thus when dynamicSRS is configured in a subframe, the base station instructs one mobileterminal to send SRS, and at the same time instructs the other mobileterminals that send data on the designated SRS resources to puncturetheir data, i.e. to not transmit data.

FIG. 6, shows the uplink transmission 504 (of FIG. 5) when thepredefined uplink symbol should be used for data transmission accordingto a first alternative (corresponding to 503 a of FIG. 5). The blacksymbols indicated as reference signals denote other reference signalsthan SRS and these other reference signals are used in all uplinktransmission. Accordingly, FIG. 6 shows the case of PUSCH transmissionwhen there is no additional transmission of SRS according to prior art,and the case when the mobile terminal is dynamically instructed to usethe predefined uplink symbol for data transmission according toembodiments of the present invention.

Further according to a second alternative (corresponding to 503 b ofFIG. 5), when the mobile terminal is to transmit additional SRS, forexample when the mobile terminal is instructed to do so dynamically e.g.by means of an indicator in the uplink scheduling grant according totechnical specification 3GPP TS 36.212 transmitted in a downlinksubframe at least three subframes earlier. The transmission of theadditional SRS is illustrated in FIG. 7.

According to a third alternative (corresponding to 503 c of FIG. 5), themobile terminal is instructed to leave the predefined uplink symbolblank, so that another mobile terminal can use the resources fortransmitting SRS. The transmission is illustrated in FIG. 8.

Turning now to FIG. 9 which provides an example to further describe theembodiments of the present invention. In the example, three mobileterminals are scheduled within one uplink (UL) subframe and dynamic SRStransmission is configured for mobile terminal 1 on the PUSCH, denotedas PUSCH 1, where the bandwidth of SRS transmission for mobile terminal1, denoted as SRS 1, covers the total bandwidth of mobile terminal 1plus the bandwidth of the mobile terminal 2. In this case the mobileterminal 1 needs to puncture its data and to insert SRS 1 at the end,the mobile terminal 2 has to puncture its data, and the mobile terminal3 can continue its normal operation as instructed by the base statione.g. by means of the UL scheduling grant. FIG. 9 illustrates thestructure of the data and the SRS.

Note that puncturing here is to be understood that data is nottransmitted. This means the code rate or the transport block size can beadapted as well. The main meaning is that no data is transmitted in thepredefined uplink symbol which instead e.g. can be used for SRS.

It should also be noted that the SRSs can be mapped to every secondsubcarrier in the frequency domain, as is the case for the soundingreference signals defined for Release 8/9 in LTE using a so calledrepetition factor of two, or be mapped to every subcarrier, as is thecase with the uplink demodulation reference signals for Release 8/9 inLTE.

The present invention may be carried out in other ways than thosespecifically set forth herein without departing from essentialcharacteristics of the invention. The embodiments described are to beconsidered in all respects as illustrative and not restrictive.

What is claimed is:
 1. A method implemented by a base station in acommunications network, the method comprising: broadcasting acell-specific instruction to a plurality of mobile terminals in a cellserved by the base station, the cell-specific instruction indicatingthat an uplink symbol has been semi-statically configured for aperiodicsounding reference signal (SRS) transmission over multiple subsequentsubframes; dynamically determining that a first mobile terminal of theplurality of mobile terminals is to use the uplink symbol for SRStransmission in a given one of the multiple subsequent subframes; and inresponse to the dynamically determining, signaling a firstterminal-specific instruction to the first mobile terminal, the firstterminal-specific instruction being distinct from the cell-specificinstruction and indicating that the first mobile terminal is to use theuplink symbol for SRS transmission in the given subframe.
 2. The methodof claim 1, further comprising, in response to the dynamicallydetermining, signaling a second terminal-specific instruction to asecond mobile terminal of the plurality of mobile terminals, the secondterminal-specific instruction being distinct from the cell-specificinstruction and from the first terminal-specific instruction andindicating that the second mobile terminal is to leave the uplink symbolin the given subframe blank.
 3. The method of claim 1, wherein saidsignaling comprises signaling the first terminal-specific instruction asdownlink control information carried by a physical downlink controlchannel.
 4. The method of claim 1, wherein the first terminal-specificinstruction is at least partially dynamically signaled in an uplinkgrant.
 5. The method of claim 1, wherein the first terminal-specificinstruction is transmitted to the first mobile terminal at a first layerof a communications protocol stack used by the base station and thecell-specific instruction is broadcast to the mobile terminals in thecell at a second layer of said protocol stack, the first layer beinglower in the protocol stack than the second layer.
 6. A methodimplemented by a mobile terminal in a communications network, the methodcomprising: receiving a cell-specific instruction indicating that anuplink symbol has been semi-statically configured for aperiodic SRStransmission over multiple subsequent subframes; receiving aterminal-specific instruction, distinct from the cell-specificinstruction, that indicates whether or not the uplink symbol is to beused by the mobile terminal for SRS transmission in a given one of themultiple subsequent subframes; determining, based on the receivedterminal-specific and cell-specific instructions, whether or not to usethe uplink symbol for SRS transmission in the given subframe; andtransmitting according to a result of the determining.
 7. The method ofclaim 6: wherein the terminal-specific instruction indicates one of:that the uplink symbol is to be used by the mobile terminal for SRStransmission in the given subframe; that the uplink symbol is to be leftblank by the mobile terminal in the given subframe to facilitate use ofthe uplink symbol for SRS transmission by another mobile terminal in thegiven subframe; and wherein the determining comprises determining oneof: to use the uplink symbol for SRS transmission in the given subframe;to leave the uplink symbol blank in the given subframe.
 8. The method ofclaim 6, wherein receiving the terminal-specific instruction comprisesreceiving the terminal-specific instruction as downlink controlinformation carried by a physical downlink control channel.
 9. Themethod of claim 6, wherein receiving the terminal-specific instructioncomprises receiving the terminal-specific instruction at least partiallyin an uplink grant.
 10. The method of claim 6: wherein the mobileterminal is served by one of a plurality of cells in the communicationsnetwork; wherein receiving the cell-specific instruction comprisesreceiving a broadcast to at least one other mobile terminal served bythe cell, the cell-specific instruction indicating to the at least oneother mobile terminal that the uplink symbol has been semi-staticallyconfigured for aperiodic SRS transmission over the multiple subsequentsubframes.
 11. The method of claim 6, wherein the terminal-specificinstruction is received at a first layer of a communications protocolstack used by the mobile terminal and the cell-specific instruction isreceived at a second layer of said protocol stack, the first layer beinglower in the protocol stack than the second layer.
 12. A base stationfor use in a communications network, the base station comprising: aprocessor configured to dynamically determine that a first mobileterminal of a plurality of mobile terminals in a cell served by the basestation is to use an uplink symbol for SRS transmission in a given oneof multiple subsequent subframes; and a transmitter configured to:broadcast a cell-specific instruction to the plurality of mobileterminals, the cell-specific instruction indicating that the uplinksymbol has been semi-statically configured for aperiodic SRStransmission over the multiple subsequent subframes; in response to theprocessor dynamically determining, signal a first terminal-specificinstruction to the first mobile terminal, the first terminal-specificinstruction being distinct from the cell-specific instruction andindicating that the first mobile terminal is to use the uplink symbolfor SRS transmission in the given subframe.
 13. The base station ofclaim 12, wherein the transmitter is further configured to, in responseto the processor dynamically determining, signal a secondterminal-specific instruction to a second mobile terminal of theplurality of mobile terminals, the second terminal-specific instructionbeing distinct from the cell-specific instruction and from the firstterminal-specific instruction and indicating that the second mobileterminal is to leave the uplink symbol in the given subframe blank. 14.The base station of claim 12, wherein the transmitter is configured toat least partially signal the first terminal-specific instruction in anuplink grant.
 15. The base station of claim 12, wherein the transmitteris configured to transmit the first terminal-specific instruction at afirst layer of a communications protocol stack used by the base stationand to broadcast the cell-specific instruction at a second layer of saidprotocol stack, the first layer being lower in the protocol stack thanthe second layer.
 16. A mobile terminal for use in a communicationsnetwork, the mobile terminal comprising: a receiver configured to:receive a cell-specific instruction indicating that an uplink symbol hasbeen semi-statically configured for aperiodic SRS transmission overmultiple subsequent subframes; receive a terminal-specific instruction,distinct from the cell-specific instruction, that indicates whether ornot the uplink symbol is to be used by the mobile terminal for SRStransmission in a given one of the multiple subsequent subframes; aprocessor configured to determine, based on the receivedterminal-specific and cell-specific instructions, whether or not to usethe uplink symbol for SRS transmission in the given subframe; atransmitter configured to transmit according to a result of thedetermining.
 17. The mobile terminal of claim 16: wherein theterminal-specific instruction indicates one of: that the uplink symbolis to be used by the mobile terminal for SRS transmission in the givensubframe; that the uplink symbol is to be left blank by the mobileterminal in the given subframe to facilitate use of the uplink symbolfor SRS transmission by another mobile terminal in the given subframe;and wherein to determine whether or not to use the uplink symbol for SRStransmission in the given subframe, the processor is configured todetermine one of: to use the uplink symbol of the given subframe for SRStransmission in the given subframe; to leave the uplink symbol blank inthe given subframe.
 18. The mobile terminal of claim 16, wherein thereceiver is configured to receive the terminal-specific instruction atleast partially in an uplink grant.
 19. The mobile terminal of claim 16:wherein the mobile terminal is served by one of a plurality of cells inthe communications network; wherein the cell-specific instruction hasbeen broadcast to at least one other mobile terminal served by the cell,the cell-specific instruction indicating to the at least one othermobile terminal that the uplink symbol has been semi-staticallyconfigured for aperiodic SRS transmission over the multiple subsequentsubframes.
 20. The mobile terminal of claim 16, wherein theterminal-specific instruction is received at a first layer of acommunications protocol stack used by the mobile terminal and thecell-specific instruction is received at a second layer of said protocolstack, the first layer being lower in the protocol stack than the secondlayer.